1. Field of the Invention
The present invention relates to a ratchet wheel with asymmetric arcuate concave teeth or non-arcuate concave teeth. The present invention also relates to a ratcheting tool, e.g., a ring spanner having a box end in which the ratchet wheel is mounted. The ratchet wheel with asymmetric arcuate concave teeth provides improved structural strength and improved torque. The ratchet wheel with non-arcuate concave teeth is easy to form and thus reduces the production cost.
2. Description of the Related Art
A wide variety of spanners and wrenches have heretofore been provided. Ring spanners are the best choice for driving fasteners (e.g., nuts, bolt heads, etc) in a limited space that is uneasy to access and difficult to operate all kinds of ratcheting tools. Nevertheless, conventional ring spanners have low driving torque. Ratchet type ring spanners have been proposed to solve this problem. A ratchet wheel is mounted in the box end of a ring spanner for driving fasteners at high torque. It is, however, found that, the structural strength of the ratchet wheel is weak, as an outer periphery of the ratchet wheel is processed to form a plurality of arcuate teeth with a considerable depth.
FIGS. 11 through 13 of the drawings illustrate a conventional ratchet wheel 1 mounted in a box end (not shown) of a ring spanner (not shown) and having an inner periphery 4 for driving a fastener (not shown) and an outer periphery having a plurality of arcuate concave teeth 3. Referring to FIG. 12, each arcuate concave tooth 3 is formed by means of feeding a cutter 2 along a direction transverse to a radial direction (see line OR). The resultant concave tooth 3 has a depth "d" and two sides that intersect at point "R". The line OR divides the angle .alpha. defined by the two sides of the arcuate concave tooth 3 into two equal portions (usually 45.degree. for each portion). As illustrated in FIG. 12, each arcuate concave tooth 3 is machined to have a considerable depth "d" that adversely affects the structural strength of the ratchet wheel 1, as the remaining wall thickness "t" of the ratchet wheel 1 is relatively small. As a result, the driving torque provided by the ratchet wheel for driving the fastener is limited.
FIGS. 14 through 16 of the drawings illustrate a conventional ratchet wheel 5 mounted in a box end 9a (FIG. 17) of a ring spanner 9 (FIG. 17) and having an inner periphery 8 for driving a fastener (not shown) and an outer periphery having a plurality of arcuate concave teeth 6. Referring to FIG. 15, each arcuate concave tooth 6 is formed by means of feeding a cutter 7 along a radial direction. The resultant arcuate concave tooth 6 has a depth "d" and two sides that intersect at point "R". The line OR divides the angle .beta. defined by the two sides of the concave tooth 6 into two equal portions (usually 45.degree. for each portion). As illustrated in FIG. 15, each arcuate concave tooth 6 is machined to have a considerable depth "d" that adversely affects the structural strength of the ratchet wheel, as the remaining wall thickness "t" of the ratchet wheel 5 is relatively small. As a result, the driving torque provided by the ratchet wheel for driving the fastener is limited. Such structure has been disclosed in U.S. Pat. No. 5,533,427 to Chow issued on Jul. 9, 1996, which is incorporated herein for reference. A further drawback of this conventional ratchet wheel is the low production rate for forming the arcuate concave teeth by cutting.
The present invention is intended to provide an improved ratchet wheel that mitigates and/or obviates the above problems.